The general procedure for the synthesis of 5-iodo-2-methoxybenzoic acid from methyl 5-iodo-2-methoxybenzoate was as follows: first, 5-iodo-2-hydroxybenzoic acid (2.81 g, 10.6 mmol) was suspended in acetone (50 ml) and potassium carbonate (K2CO3, 6.77 g, 49.0 mmol) was added. The reaction mixture was cooled in an ice water bath, followed by the slow addition of dimethyl sulfate (2.4 ml, 25 mmol) via syringe. After the reaction mixture was gradually warmed to room temperature, it was heated to reflux and stirred continuously overnight. After 14.75 hours of reaction, it was cooled to room temperature, diluted with water (150 ml) and stirring was continued for 30 minutes. Next, extraction was carried out with ethyl acetate (EtOAc, 3 x 50 ml), the organic phases were combined, dried with magnesium sulfate, filtered and concentrated, and finally purified by silica gel column chromatography (using a Biotage apparatus with an elution gradient of 5% ethyl acetate/hexane to 100% ethyl acetate) to give methyl 5-iodo-2-methoxybenzoate (3.08 g, 99% yield). Subsequently, the product was dissolved in methanol (MeOH, 25 ml) and 1N sodium hydroxide solution (15 ml, 15 mmol) was added. The reaction was stirred at room temperature for 2 h before supplemental addition of methanol (8 ml) and 1N sodium hydroxide solution (8 ml, 8 mmol). The reaction system was heated to 60 °C and stirring was continued for 2.25 h, after which it was cooled to room temperature. The reaction mixture was filtered and the solid product was collected and dried under vacuum to give the target compound 5-iodo-2-methoxybenzoic acid (2.75 g, 94% yield). Mass spectrometric analysis (ESI positive ion mode) showed m/z: 279 ([M+H]+). the theoretical exact mass of C8H7IO3 was 278.
